Buggy code:
@ Override public IRubyObject inspect ( ) { } @ JRubyMethod ( name = "inspect" ) public IRubyObject inspect19 ( ) { } public static IRubyObject inspect19 ( Ruby runtime , ByteList byteList ) { } public int size ( ) { } public RubyFixnum length ( ) { } @ JRubyMethod ( name = { "length" , "size" } ) public RubyFixnum length19 ( ) { } @ JRubyMethod ( name = "bytesize" ) public RubyFixnum bytesize ( ) { } private RubyEnumerator . SizeFn eachByteSizeFn ( ) { } @ JRubyMethod ( name = "empty?" ) public RubyBoolean empty_p ( ThreadContext context ) { } public boolean isEmpty ( ) { } public RubyString append ( IRubyObject other ) { } public RubyString append19 ( IRubyObject other ) { } public RubyString concat ( IRubyObject other ) { } @ JRubyMethod ( name = { "concat" , "<<" } ) public RubyString concat19 ( ThreadContext context , IRubyObject other ) { } private RubyString concatNumeric ( Ruby runtime , int c ) { } @ JRubyMethod public IRubyObject prepend ( ThreadContext context , IRubyObject other ) { } @ JRubyMethod ( name = "crypt" ) public RubyString crypt ( ThreadContext context , IRubyObject other ) { } public static RubyString stringValue ( IRubyObject object ) { } public IRubyObject sub ( ThreadContext context , IRubyObject arg0 , Block block ) { } public IRubyObject sub ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } public IRubyObject sub_bang ( ThreadContext context , IRubyObject arg0 , Block block ) { } public IRubyObject sub_bang ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } @ JRubyMethod ( name = "sub" , reads = BACKREF , writes = BACKREF ) public IRubyObject sub19 ( ThreadContext context , IRubyObject arg0 , Block block ) { } @ JRubyMethod ( name = "sub" , reads = BACKREF , writes = BACKREF ) public IRubyObject sub19 ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } @ JRubyMethod ( name = "sub!" , reads = BACKREF , writes = BACKREF ) public IRubyObject sub_bang19 ( ThreadContext context , IRubyObject arg0 , Block block ) { } @ JRubyMethod ( name = "sub!" , reads = BACKREF , writes = BACKREF ) public IRubyObject sub_bang19 ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } private IRubyObject subBangIter19 ( Ruby runtime , ThreadContext context , Regex pattern , Regex prepared , RubyHash hash , Block block , RubyRegexp regexp ) { } private IRubyObject subBangNoIter19 ( Ruby runtime , ThreadContext context , Regex pattern , Regex prepared , RubyString repl , RubyRegexp regexp ) { } private IRubyObject subBangCommon19 ( ThreadContext context , Regex pattern , Matcher matcher , RubyString repl , int tuFlags ) { } private Encoding subBangVerifyEncoding ( ThreadContext context , RubyString repl , int beg , int end ) { byte [ ] bytes = value . getUnsafeBytes ( ) ; int p = value . getBegin ( ) ; int len = value . getRealSize ( ) ; Encoding strEnc = value . getEncoding ( ) ; if ( ( ( StringSupport . codeRangeScan ( strEnc , bytes , p , beg ) ) != ( StringSupport . CR_7BIT ) ) || ( ( StringSupport . codeRangeScan ( strEnc , bytes , ( p + end ) , ( len - end ) ) ) != ( StringSupport . CR_7BIT ) ) ) { <START_BUG> throw context . runtime . newArgumentError ( ( ( ( "incompatible<seq2seq4repair_space>character<seq2seq4repair_space>encodings<seq2seq4repair_space>" + strEnc ) + "<seq2seq4repair_space>and<seq2seq4repair_space>" ) + ( repl . value . getEncoding ( ) ) ) ) ; <END_BUG> } return repl . value . getEncoding ( ) ; } public IRubyObject gsub ( ThreadContext context , IRubyObject arg0 , Block block ) { } public IRubyObject gsub ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } public IRubyObject gsub_bang ( ThreadContext context , IRubyObject arg0 , Block block ) { } public IRubyObject gsub_bang ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } @ JRubyMethod ( name = "gsub" , reads = BACKREF , writes = BACKREF ) public IRubyObject gsub19 ( ThreadContext context , IRubyObject arg0 , Block block ) { } @ JRubyMethod ( name = "gsub" , reads = BACKREF , writes = BACKREF ) public IRubyObject gsub19 ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } @ JRubyMethod ( name = "gsub!" , reads = BACKREF , writes = BACKREF ) public IRubyObject gsub_bang19 ( ThreadContext context , IRubyObject arg0 , Block block ) { } @ JRubyMethod ( name = "gsub!" , reads = BACKREF , writes = BACKREF ) public IRubyObject gsub_bang19 ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block ) { } private IRubyObject gsub19 ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 , Block block , final boolean bang ) { } private IRubyObject gsubCommon19 ( ThreadContext context , Block block , RubyString repl , RubyHash hash , IRubyObject arg0 , final boolean bang , int tuFlags ) { } private IRubyObject gsubCommon19 ( ThreadContext context , Block block , RubyString repl , RubyHash hash , IRubyObject arg0 , final boolean bang , int tuFlags , boolean useBackref ) { } public IRubyObject index ( ThreadContext context , IRubyObject arg0 ) { } public IRubyObject index ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 ) { } @ JRubyMethod ( name = "index" , reads = BACKREF , writes = BACKREF ) public IRubyObject index19 ( ThreadContext context , IRubyObject arg0 ) { } @ JRubyMethod ( name = "index" , reads = BACKREF , writes = BACKREF ) public IRubyObject index19 ( ThreadContext context , IRubyObject arg0 , IRubyObject arg1 ) { }

Fix:
throw context . runtime . newEncodingCompatibilityError ( ( ( ( "incompatible<seq2seq4repair_space>character<seq2seq4repair_space>encodings<seq2seq4repair_space>" + strEnc ) + "<seq2seq4repair_space>and<seq2seq4repair_space>" ) + ( repl . value . getEncoding ( ) ) ) ) ;